The invention concerns a cooling system for a gantry and a computer tomography system with an x-ray source, positioned in a gantry housing and rotatable around a rotation axis, in which the gantry housing is positioned at a stationary part of the computer tomography system so that it can be moved, in particular pivoted, by means of at least one bearing. Moreover, the invention concerns a corresponding method to cool such a gantry.
In computer tomography systems, three-dimensional slice images of the inside of an examination subject are generated with the aid of an x-ray method. For this, by means of a scanning unit—in general called a gantry—which comprises an x-ray source normally rotating around the acquisition subject and an image acquisition system, two-dimensional x-ray slice images are generated from which a three-dimensional slice image is reconstructed. The gantry is typically located in a gantry housing which is annularly arranged around an examination subject acquisition space. In computer tomography systems of the previously cited type, a tilting of the image plane relative to the examination subject can additionally be achieved by pivoting the gantry housing or, respectively, the gantry, in order to achieve, for example, a slice direction parallel to the subject surface. In this manner, for example, arbitrary coronary slices can be created.
A basic problem in all x-ray systems is that 99% of the electrical energy used in the generation of the x-ray radiation in the x-ray source is transduced into heat energy. This heat accumulating in the operation of the x-ray source must be dissipated from the x-ray source in order to be able to operate the x-ray source over a longer span of time without an overheating of the source. This is in particular necessary when high x-ray densities are required. In computer tomography systems of the previously cited type, it additionally aggravates matters that the x-ray source continuously rotates in the gantry housing around the examination subject acquisition space during a radiological exposure. Due to this continuous rotation movement, the extremely high temperatures and the narrowness of the inner space of the gantry housing, the dissipation of the heat accumulating in the operation of the x-ray system proves to be complicated and problematic.
The cooling systems used until now in such computer tomography systems are for the most part formed of a plurality of heat exchangers that are installed inside the gantry housing. In order to dissipate the heat accumulating at the rotating x-ray source from the gantry and from the inside of the gantry housing as efficiently as possible, conventionally a heat exchanger is mounted in direct proximity to the x-ray source and rotating with it. This first heat exchanger dissipates the heat to the air surrounding the gantry in the gantry housing. The heated air around the gantry can, for example, by cooled by a second heat exchanger which dissipates the heat acquired from the air to a cooling system outside of the gantry housing. Allowed U.S. patent application Ser. No. 09/664,338, whose disclosure is incorporated herein by reference thereto and which claims priority from DE 199 45 413, shows a computer tomography system in which the second heat exchanger is arranged stationary in the gantry housing relative to the x-ray radiator. The heat acquired during the operation by the second heat exchanger is dissipated by coolant lines to a cooling system outside of the gantry housing. U.S. Pat. No. 6,412,979, whose disclosure is incorporated herein by reference thereto and which claims priority from DE 198 45 756, offers an alternative. In the computer tomography system shown there, the second heat exchanger is arranged in the gantry housing, rotating with the gantry. The dissipation of the heat ensues during the idle periods [downtimes; standstill periods] of the gantry between two measurements, in which the second heat exchanger is coupled by means of a rapid coupling with a water cooling circuit or loop arranged outside of the gantry housing.
It proves to be disadvantageous in the cited cooling systems that a plurality of precise mechanical and electrical components are necessary that, due to their function, tend to wear out and must be correspondingly maintained. A further disadvantage is that the gantry housing must be correspondingly, voluminously dimensioned, due to the size of the required heat exchanger. However, quite good cooling capacities can be achieved with the last described variant. However, it has a what is disadvantage which is that the cooling of the coolant is possible only given sufficient idle periods. Moreover, the pivotable realization of the gantry housing is hampered due to the necessary coupling to an external coolant circuit.